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Re: birds/dino-birds with teeth



On Sat, May 04, 2002 at 11:26:52AM +0200, David Marjanovic sent:
> > I don't know why a beak would extend progressively further from the
> > labial margin of the (pre)maxilla/dentary in a protobird. Though I
> > can say that the usefulness of teeth would be reduced once the beak
> > impeded their ability to sink into flesh. If the first beaked
> > animals were insectivorous, I don't suppose teeth would be greatly
> > needed.
> 
> I agree. Another possibility might be that a beak provides a smooth
> cutting edge if it's toothless; this might apply to confuciusornithids
> with their strong, akinetic skulls (Feduccia thinks they were
> folivores, much like a hoatzin... who knows). But then the toothless
> pmx of Hesperornithiformes and Ichthyornithidae is totally
> counterintuitive... or means that they inherited this feature from an
> ancestor which did something else with its beak.

Teeth have a cost; you have to grow them.  If you're a theropod with
teeth that undergo regular replacement, you have to _keep_ growing them.

When you're a relatively large flesh eating animal, the mineral and
metabolic cost isn't that high; when you're a relatively small animal,
and not flesh eating the mineral and metabolic cost is proportionately
higher.  If you're a relatively small animal under selection pressure to
grow to mature size rapidly, any metabolic cost related to the growth
process which can be got rid of is likely a net win.

Toothlessness in birds probably goes with rapid hatchling growth.

-- 
graydon@dsl.ca   |  Hige sceal þe heardra, heorte þe cenre,
                 |  mod sceal þe mare þe ure maegen lytlað.
                 |   -- Beorhtwold, "The Battle of Maldon"